Necrosis is the death of tissues of part or a whole organ of the living body.
Causes of necrosis are as follows:
• physical
• high or low temperatures;
• radiation or electrical energy (see «Thermal injuries»);
• chemicals.
• Mechanical
• pressure on or crushing of tissues (see «Closed injuries to soft tissues»).
These types of injury directly lead to necrosis of tissues. Local circulatory disorders (e.g. thrombosis, embolism or vascular occlusion) often result in indirect necrosis. The condition is accompanied by abnormal innervation when the nerves are damaged (e.g. leprosy, syringomyelia).
Necrosis can be:
• coagulative, or dry (burns, dry gangrene);
• colliquative, or wet (alkaline burns, wet gangrene).
The signs of necrosis become obvious within 4 to 6 hours after tissue death. The necrotic tissue undergoes rejection and, if located on the surface of an organ, an ulcer develops. Extensive necrosis with widespread tissue decay results in systemic absorption of toxic products, which, in turn, leads to intoxication.
GANGRENE AND VARICOSE (STASIS) ULCERS
Necrosis due to primary blood circulatory disorders is referred to as gangrene.
Causes:
• extensive crushing;
• severe pressure on tissues;
• vascular injuries;
• organ compression (e.g. POP bandage);
• volvulus with compression of the vessels;
• leaving the tourniquet on a limb for a long time;
• vascular thrombosis and embolism;
• obliterating endarteritis;
• obliterating arteriosclerosis.
Most commonly acute and chronic arterial occlusion lead to gangrene.
Dry gangrene is caused by fast dehydration of the necrotic tissues without bacterial contamination.